ignimbrites (metaignimbrites) of lower Ordovician age (Tremadocian). Its mineralogy is composed of phenocrysts of quartz, alkali feldspar and plagioclase (albite) and a very fine-grained matrix (grain-size 5 μ) made of quartz, feldspars, sericite and rare chlorite. Original fiamme are hard to discern, but welded glassy layers are recognisable. The metaignimbrite is rich in potassium and contains more than 70% of SiO2. Underlying the Génis porphyroid are the Donzenac schist and the Thiviers sandstone, the main formations of the Thiviers-Payzac Unit. In the Fugeyrollas anticline the Thiviers sandstone appears on the surface and thus also crops out within the Génis Unit. Both formations are supposed to cover the age range Neoproterozoic to Cambrian. Structural organisation The Génis Unit is thoroughly folded into tight, upright folds with a wavelength of about 150 meters. The fold axes strike WNW-ESE (N 110) with a slight dip of about 10 ° to the east. The original sedimentary layering (S0) can often still be recognised dipping 75 to 80 ° to the north or to the south. Parallel to the folds' axial plane a distinct schistosity has developed (S1). The tight folds are overprinted by secondary folding and deformed into large anticlines and synclines with a wavelength of about 2 kilometers (Cubas syncline in the south followed by the Fougeyrollas anticline and the Génis syncline to the north). Imprinted on the layering are well developed stretching lineations also running more or less parallel to the fold axes. Newly formed metamorphic minerals are preferably arranged along this direction, although their lineations stray between N 110 and N 135. Furthermore the lineations are accompanied by microfolds, whose axes yet again follow the N 110-direction. Metamorphism and structural evolution During the Variscan orogeny the original sedimentary succession of the Génis Unit subsided and was metamorphosed due to increasing overburden. The metamorphism followed a retrograde path (neoformation of chlorite) and recorded the epizonal conditions of the greenschist facies. This fact is very important for the geology of the Massif Central, because low-grade metamorphic successions are underrepresented and quite rare. Usually the metasediments in the Massif Central are strongly deformed and metamorphosed (under amphibolite facies conditions) and therefore only rough guesses can be made about their protoliths. The retrograde metamorphism is known in other places of the Massif Central and is assigned a mid-Carboniferous age. Like the already mentioned South Limousin Fault the entire Génis Unit underwent ductile, dextral wrenching and